As a popularization of digital devices and information terminals advances, a touch panel is often used as one of input devices for performing a data entry in mobile terminals (e.g., smartphones), computers, electronic diaries, portable game devices, digital cameras or the like. The touch panel has a high transparency, and is capable of providing an intuitive operation for data entry by sensing the position of a finger or pen when it comes into contact with or comes into vicinity of an input surface of the panel.
It is required for the transparent electrode used for the touch panel to have not only a high light transmittance regarding a visible light region, but also a high electrical conductivity. Such transparent electrode is also used as an electrode of solar batteries, liquid crystal display elements and other various light-receiving elements, as well as antistatic films. The transparent electrode having the low resistance is needed especially in the fields of solar batteries, display elements (e.g., liquid crystal, organic electroluminescence and inorganic electroluminescence) and touch panels used therefor.
As a material for a transparent electrically-conductive thin film of such transparent electrode, ITO (i.e., indium oxide containing a tin as a dopant) is now most commonly used from an industrial perspective. The film made of such ITO has a particularly low resistance and is easy to produce. However, there has been a concern about the depletion of an In element which is used as a main element of the ITO. Therefore, there has been recently carried out a research regarding alternatives to the ITO, i.e., the research regarding film-formable materials having not only a transparency but also an electrical conductivity.
As a metal oxide for the alternative to the ITO, there have been used a tin oxide (SnO2), an ATO where an antimony is contained therein as a dopant, and a FTO where a fluorine is contained therein as a dopant. There have also been used a zinc oxide (ZnO), an AZO where an aluminum is contained therein as a dopant, and a GZO where a gallium is contained therein as a dopant. See Patent Documents 1 and 2, for example.
In order to produce a transparent electrode from such metal oxide, there have often been employed physical film-forming methods such as a deposition method, a sputtering method and an ion-plating method, or chemical film-forming methods such as a chemical vapor deposition (CVD) method. However, these methods are accompanied by problems that not only a production cost is higher due to a significantly low film-forming rate, but also the size of the formed film is restricted by the size of a vacuum vessel of a vacuum apparatus, which fails to manufacture a large-sized transparent electrode.